Silver Nanoparticles: No Threat to the Environment

Silver is an effective germ fighter and silver nanoparticles are widely recognized as being especially effective because of their enormously high surface area. Due to the large number of manufacturers using silver nanoparticles in their products, some concern has arisen about the effects on the environment when these products are disposed of or washed. This report will demonstrate that silver nanoparticles do not remain “nanosize” when they come in contact with normal environmental samples, such as soil and water, but they agglomerate to form much larger, much less biologically effective, silver particles which are non-toxic, non-ionic and have no history of being harmful to the environment or aquatic life. Furthermore, there is no possibility that silver nanoparticles can ever form silver ions, except in the presence of strong oxidizing substances.

Recently, the Environmental Protection Agency (EPA) issued a statement that they were planning to regulate companies that produce nanoparticles for use as antimicrobials. This gives rise to the question: why are the dietary supplement and nanoparticle industries being targeted at this time and what is the rational for new regulation of an industry which has previously had no reported harmful effects to humanity or the environment?

The EPA knows that silver nanoparticles are effective as antimicrobials. The reason given by the EPA for the current interest is that silver nanoparticles, or products that claim to be silver nanoparticles, are now being produced by a number of manufacturers, and the EPA is concerned that, when these particles are disposed of, there might be an appreciable amount of silver nanoparticles suddenly appearing in the environment. The proposed concern is due to the fact that the silver nanoparticles are so small that their surface area per unit weight is very large, therefore, for a given weight of product, the biological effectiveness, which is proportional to surface area, is far beyond that which would be expected. This much is true and it is part of the reason that silver nanoparticles are so attractive in biological applications. The EPA is not questioning the fact that silver nanoparticles are effective in killing harmful bacteria, but that, because of the high surface area/weight effectiveness parameter, by disposing these particles into sewers or waterways, might there be harmful effects to the environment by eliminating the bacteria which are useful in normal waste degradation?

The last statement shows a misunderstanding of what silver nanoparticles are and what they do. Nanoparticle technology is relatively new to the scientific community for good reasons: Nanoparticles are difficult to produce; they are difficult to stabilize once they have been produced; they are not stable enough to exist in nature for very long. The purpose of this work is to prove that normal interaction of nanoparticles with various © 2008 Colloidal Science Lab., Inc. soils and different water sources is sufficient to change the size and dramatically decrease the biological activity. Specifically, the areas of examination will include experiments which will establish that silver colloids, which start out as nanoparticles, upon contact with the environment “grow” to much larger clusters, as indicated by their average particle size distribution, (a nanoparticle size measurement), and zeta potential measurements, which will establish that the zeta potential is outside of the range required for nanoparticle stability.